1. Field of the Invention
The present invention relates to a reciprocating type compressor. More particularly, it pertains to a structure of pressure passages between chambers in a reciprocating type compressor which employs a drive plate to compress refrigerant gas.
2. Description of the Prior Art
In a compressor which employs a drive plate such as a swingable swash plate, the drive plate is mounted on a rotation shaft inside a crank chamber. The rotation of the shaft is converted to the reciprocating movement of pistons in associated cylinder bores by the drive plate. The refrigerant gas, supplied to the cylinder bores from a suction chamber, is compressed by the reciprocating movement of the pistons and then discharged from the compressor via a discharge chamber. Since the crank chamber is defined in a tightly sealed space, it is necessary to maintain the pressure of the chamber within a proper range.
However, a leakage, or blow-by, of compressed gas occurs between the outer cylindrical surface of the pistons and the inner cylindrical surface of the respective cylinder bores. The blow-by gas infiltrates the crank chamber and raises the pressure within. Furthermore, in a variable type compressor, which automatically adjusts an inclining angle of the drive plate, the discharge volume of the compressor is changed by automatically adjusting the pressure inside the crank chamber according to a cooling load. Accordingly, compressors having a structure which discharges the pressure within the crank chamber into other chambers have been proposed. These compressors communicate the crank chamber with the discharge chamber or suction chamber for releasing of the pressure.
Japanese Examined Patent Publication 3-55675 discloses such a compressor. In this compressor, a gas bleeding passage is formed between the suction chamber and the crank chamber. A blow-by of the refrigerant gas in the crank chamber, from the compressing chambers of the cylinder bores, is returned to the suction chamber via the passage. This prevents excessive pressurizing of the crank chamber caused by the blow-by.
In addition, an air intake passage, provided with a release valve, is formed between the discharge chamber and the crank chamber. The valve has a valve control mechanism on which the pressure of the crank chamber acts by way of a pressurizing passage. The opening and closing of the valve is controlled by the mechanism according to the pressure within the crank chamber. The opening and closing of the valve adjusts the pressure inside the crank chamber. This alters the inclining angle of the swing swash plate and controls the discharge volume of the compressed gas.
However, in the above compressor, the gas bleeding passage and the pressurizing passage are formed between neighboring cylinder bores extending along the full length of a cylinder block in its axial direction. Normally, these passages are 2 to 4 mm in diameter and 40 to 50 mm in length. To form these passages which have a long length and small diameter, a drill having a long length and small diameter is required. Therefore, there are cases in which the drill breaks during the formation of these passages. As a result, the machining of these passages is very difficult and troublesome. In addition, means to detect the breakage of the drill such as sensors may become necessary. This raises equipment costs.